A hip joint is a heavily stressed, load-carrying bone joint in the human body. It is essentially a ball and socket joint formed by the top of the femur which pivots within a cup-shaped acetabulum at the base of the pelvis. When a break or fracture occurs adjacent to the top of the femur, the separated portions of the femur must be held together while healing occurs.
There have been a number of techniques used historically for treatment of fractures of the proximal and distal ends of the femur. In early parts of this century, patients were merely placed in bed or in traction for prolonged periods, frequently resulting in deformity or death. In the 1930s, the Smith-Peterson nail was introduced, resulting in immediate fixation of hip fractures, early mobilization of the patient, and a lowered morbidity and mortality. A number of nails have been introduced for a fracture fixation about the femur in its proximal end, including the Jewett nail and, in more recent years, dynamic compression devices that allow capture of the most proximal fragments of the femur, compression of intertrochanteric and subtrochanteric fracture fragments, rigid fixation of the most proximal and distal fragments, and a sliding lag screw or anchor which fits within a barreled side plate for allowing further compression of fragments as the patient ambulates and begins to bear weight on the fractured limb. The side plate is typically secured to the bone fragment with a series of screws or fasteners.
The use of a rigid, blade plate, has been used both at the proximal end of the femur for fixation of subtrochanteric femur fractures, and at the distal end for fixation of supracondylar and intercondylar fractures about the knee. Because these fractures can be technically challenging to fix, a dynamic compression screw, similar in many respects to a dynamic hip compression screw, but with a side plate design and angle similar to a blade plate, have been utilized for several years.
All of the known prior art, whether in the patient literature as described above, or in commercial devices, fails to take into account the shifting of the lag screw or anchor and its compression screw in the barrel as the break heals and the fragments move closer together. When this movement occurs, the compression screw can back out of the lag screw and move away from the break and into the soft tissue causing discomfort, pain and a painful bursa. With osteogenic patients, the dynamic hip compression screws can loosen or erode through the superior bone of the head of the femur, resulting in joint penetration and destruction of the joint, producing arthritis. This can necessitate additional surgery for the removal of the hip compression screw, and replacement of the hip with a prosthesis. Similarly, the use of a dynamic compression screw in osteogenic patients may result in inadequate purchase of the lag screw threads within the bone. With loss of purchase of the lag screw or anchor within the head of the femur, compression forces are dissipated, and the implant device can fail, resulting in a nonunion or malunion of the fracture fragments. Similar loss of fixation can occur about the supracondylar and intercondylar fractures of the distal femur with osteogenic patients.
To prevent loss of fixation with compression and to decrease required removal of the anchoring lag screw within the femoral head in osteogenic patients, some devices have been modified to increase purchase of the anchoring lag screw within the femoral head, by enlarging the lag screw, or by alternative means of fixation of the proximal fragment with a molley bolt concept. This later device has not gained as wide an acceptance with surgeons in the United States as it differs from traditional lag screw techniques of screwing in the device, giving the surgeon a sense of "feel" of the degree of purchase of the lag screw with the bone, and thus, an idea of the degree to which the surgeon may compress the lag screw and side plate assembly without loss of fixation by "over-compression".
As the lag screw slides within the barrel of the side plate, it can become prominent on the side of patients who are cachectic. Frequently, the compression screw will back out once implanted, leading to further prominence of the device and possible erosion through the skin. This can lead to premature or unwanted additional surgery for removal of the compression screw or device increasing the morbidity, rate of infection and mortality caused by additional surgery, frequently in frail elderly patients who are least able to withstand additional surgical insult to their body. Many surgeons remove the compression screw for this very reason, to prevent it from backing out. With removal of the compression screw, however, the possibility of disassembly of the device can occur with resultant failure of fracture fixation and the necessity for further surgical operations. Some hip pinning systems have been modified to prevent the inadvertent disassembly of the lag screw and side plate by constraining the degree to which the lag screw and side plate can dissociate and by increased modularity of the side plate and lag screw component, enabling perhaps a smaller incision on the patient. This modularity, however, introduces another theoretical variable of potential loss of fixation of the side plate in the lag screw portions of the devices. Furthermore, the side plates can loosen their purchase from the distal fragments by biological resorption with resultant loss of purchase of fixation of the screws holding the side plate to the lateral side of the femur. This can happen in either the dynamic hip compression screws or the dynamic compression screws used about distal condylar fractures of the femur or for subtrochanteric fractures of the femur. Closer placement of the screw holes in the side plate, enabling more threads per unit of length of the femur, or alternating the number and location of holes in the side plate with a broader side plate have been advocated to reduce the incidence of loss of purchase of the side plate. The use of a distal compression screw allows more proximal compression in the longitudinal axis of the femur, to increase compression at the fracture site.
Furthermore, the screws or fasteners used to hold the side plate to the lateral femur often become loose as bone is resorbed about the external threading on the screws. Thus, the side plate often becomes loose from the bone, resulting in failure of the implant and loss of fixation of the fracture.
Thus, there is a need for an improved hip pinning or surgical fastener assembly that allows greater purchase of the lag screw within the femoral head of the hip bone while yielding a "feel" of fixation to the surgeon during insertion of the lag screw.
Such a pinning system for fixation assembly should furthermore be designed to allow a compression screw to remain permanently in place after surgery thus maintaining the degree of compression between the lag screw and side plate. It is also desirable to prevent the screws used to maintain the side plate in fixed relation relative to the bone fragment from loosening thereby maintaining the side plate in secure relation relative to the bone to which it was initially secured.